The present invention relates to a method and apparatus for developing heat within conductive materials and more particularly to such a method and apparatus wherein a large portion of the heat is developed by I.sup.2 R heat energy within the material itself.
Numerous applications call for developing heat within a conductive material. Well-known examples of such applications include pipe-fitting wherein solder is melted to join copper pipe, sheet metal fastening wherein seams and overlaps are soldered, and thawing sections of frozen water pipes. Other less common applications of the present invention may include developing heat within such substances as fused electrolytes, semiconductors, powders, and mixes for whatever purpose necessary.
The best known method of heating in an application such as pipe-fitting and so forth is the use of a blow torch. The open flame produced by a blow torch, however, poses a conspicuous fire hazard, especially when used in proximity to combustible materials. To alleviate the safety hazards associated with blow torches, a number of different techniques have been proposed for electrically heating conductive materials. Such techniques typically involve the heating of resistive heating elements and conduction of heat from the heating elements to the work-piece. Because of thermal losses and poor heat transfer to the workpiece, the efficiency of such techniques is generally quite low and the time required to heat up the work-piece rather prolonged. Techniques are known wherein heat is generated in heating elements held in contact with a work-piece by the flow of electric current serially through the heating elements and the work-piece itself, as for example in U.S. Pat. No. 2,139,499. Such techniques have not concerned themselves, however, with maximizing the current through the work-piece such that the speed and efficiency of the heating operation may be optimally increased.